Show an error/warning message when using user-specific search filters while logged out

[dfabulich]

There are a bunch of search filters that only do anything useful if you're logged in:

• played
• willplay
• wontplay
• reviewed
• rated

If you use them while logged out, they just silently don't do anything. But perhaps the UI should include a warning about this? An error, instead of search results?

(And what about the search API?)

[dfabulich]

This would affect the home page's "IFDB recommends" search: played:no willplay:no wontplay:no reviewed:no rated:no